Pontchartrain estuary atlas 2017

The 2017 Pontchartrain Estuary Atlas

Introduction & Synopsis

The thirty-six maps included in the 2017 Pontchartrain Estuary Map Atlas represent LPBF’s current understanding of the estuary for 2017. The Atlas was composed utilizing data and analyses from an array of ongoing projects, but most significantly LPBF’s 2017 Hydrocoast maps which are a suite of five maps produced biweekly that are intended to give continuous “snap shots” of the estuary. Given enough snap shots, this becomes a “movie”, and movie tells a narrative that begins to suggest estuarine trends and future conditions. The Atlas is intended to summarize the year of general conditions and indicate possible trends.

The two constructed structural closures in the MRGO shipping channel were completed in 2009, and so, the 2017 Atlas represents conditions eight years after closure. There are compelling data that demonstrate that the closure in 2009 has affected surface water salinity over approximately 1.2 million acres or about 20% of the Lake Pontchartrain Basin. The Atlas represents some conditions which may have now stabilized to a new baseline (such as surface water), but other conditions are still adjusting to the new hydrological and surface water conditions, such as soil salinity, wetland habitat, and fisheries.

The Pontchartrain Estuary Atlas area is 5,489 square miles and represents 58% of the total Lake Pontchartrain Basin. The geographic boundaries of the Pontchartrain Estuary are the Mississippi River, the Chandeleur Islands, the LA/MS state line in Mississippi Sound (an arbitrary jurisdictional boundary), and the upper limits of the coastal zone around Lakes Pontchartrain and Maurepas. The estuary can be subdivided hydrologically into two sub-basins. The estuary north of the MRGO functions hydrologically independent of the area south of the MRGO. The two sub-basins are defined by the MRGO levee and spoil bank which act as a hydrological barrier between the two areas. Fortuitously, the MRGO barrier effect emulates what would otherwise be the natural hydrological barrier of the historic ridges of Bayou la Loutre and Bayou Terre aux Bouefs, which are now compromised with canals through the natural ridges.

Wetland Land Change 2006 - 2016

Wetland land change (gain and loss) since 2006 has been modest. The areas of largest loss were southwest of Lake Lery which seems to have occurred during Hurricane Gustav (2008). Post-MRGO closure in 2009 and post- Hurricane Isaac (2012), the region appears to be stable, except for local land growth near river outlets such as the Caernarvon Freshwater Diversion, Mardi Gras Pass, and Baptiste Collette.

To learn more about the MRGO Closure, Caernarvon Freshwater Diversion, and Mardi Gras Pass, please see:

Land Change 2009 - 2016

Percent Land Change per Km² 2006 - 2016

Percent Land Change per Km² 2009 - 2016

Percent Land Change per Km² with Average Annual Discharge 2013 - 2016

Surface water salinity

Based on surface water salinity, the estuary falls into the estuarine habitats listed below, but it should be noted that wetland vegetation types do not fully match this surface water salinity regime (see soil salinity and wetland habitat types discussions).

These areas of saltwater movement result in larger surface water salinity deviations seen in 2017 (standard deviation ~ 7 ppt). The salinity incursions are seasonally moderated by either Pearl River discharge or by discharges from the Mississippi River.

To view biweekly snapshots of salinity, biological, water quality, habitat, and weather conditions of the Pontchartrain Basin, please see:

2017 Minimum Surface Water Salinity

2017 Average Surface Water Salinity and 2017 Cumulative Freshwater Discharge

2017 Average Surface Water Salinity and 2017 CRMS Station Surface Water Salinity

soil porewater salinity

Soil salinity is only collected in wetland areas. It is not collected in water bottoms of lakes or sounds. Wetland soil salinity generally reflects an estuarine gradient similar to surface water but, in some locations, seems to have lingering effects of the prior higher surface water condition of the estuary when the MRGO was open from 1965 to 2009. The Maurepas Land Bridge has areas with soil salinity over 2.0 ppt even though surface water salinity has been less than 1.0 ppt for over two years. The west side of the Biloxi marsh has a residual high soil salinity halo. In both cases, soil salinity has decreased since 2016, and CRMS data show soil salinity decreasing since 2009 for much of the Pontchartrain Basin. Overall, mean surface water salinity is lower than mean soil salinity in 2017 for 90% of the Lake Pontchartrain Estuary.

Change in Average Soil Salinity from 2016 to 2017

2017 Soil Salinity and CRMS Station Soil Salinity

bottom water hypoxia

Hypoxia occurs annually in the spring and summer in Chandeleur Sound and Breton Sound. The hypoxia most likely develops due to different drivers in the two areas, and the hypoxic areas may converge at times. Both regions show stratification but often at different depths and with different salinity patterns. Chandeleur Sound hypoxia originates in the deep pass between Chandeleur Island and Ship Island. It then appears to expand westward into Mississippi Sound and southward into Chandeleur Sound. Breton Sound hypoxia seems to stem from the influx of Mississippi River water and associated nutrients in the vicinity of Ft. St. Philip, and spreads northward toward Chandeleur Sound.

For more information about hypoxia in Chandeleur and Breton Sounds, please see:

Hypoxia Survey: July 7th and 11th, 2017

Hypoxia Survey: September 18th and 19th, 2017

Observed Hypoxic Area by Month- 2017

Cumulative of Hypoxic Areas Surveyed in 2017

Cumulative Hypoxia 2008 - 2017

Oyster habitat suitability

Oyster suitability analysis (based on surface water salinity only), indicates, that post-MRGO closure, oyster propagation has improved in the Biloxi Marsh and declined south of the MRGO. Oyster fleet activity generally corresponds to the area of good oyster habitat. However, there is indication that good habitat may extend further eastward into Chandeleur Sound, an area of underutilized potential to propagate oysters or a viable target for future oyster reef restoration.

Oyster Harvesting Fleet Density 2017

Brown & White shrimp fishery

The highest densities of the brown and white shrimp fleet are located on the outer fringes of the Biloxi Marsh where it meets Chandeleur Sound, outer fringes of the Breton Marsh just north of Pointe à la Hache, around the Mississippi River Delta, and in Lake Borgne. During the spring brown shrimp season (May – June) fleet activity was located in salinities between 0.5 - 16 ppt, with a majority of the activity located in waters with a salinity of 12 ppt or less. During the fall white shrimp season (August – November) the fleet activity was located in salinities between 1 - 21 ppt, with a majority of the activity in waters with a salinity 10 ppt or less. The Pontchartrain Estuary also experienced more fleet activity during the brown shrimp season.

Brown Shrimp Fishery Fleet Density with May - June 2017 Average Surface Salinity

White Shrimp Fleet Density with August - November 2017 Average Surface Salinity

Wetland Vegetation Change

Soil salinity isohalines from 2017 follow patterns of wetland types mapped in 2013 by the USGS. However, in 2017, several areas in the basin were exposed to soil salinity and surface water salinity that is fresher than would be expected for the wetland type that was mapped in 2013. In part, this may be explained by the time difference in data sets. Because of the MRGO closure, the soils and vegetation, which tend to change more slowly than surface water, are still transitioning towards the fresher conditions of the surface water. Along the Mississippi River, habitats are also freshening due to increase discharge from Ft. St. Philip and Mardi Gras Pass.

2017 Soil Salinity Range Compared to 2013 Wetland Vegetation Type

2017 Soil Porewater Salinity Contours over 2013 Wetland Habitat Type

swamp restoration suitability

Swamp restoration suitability analysis uses surface water and soil porewater salinity data from two consecutive years, and other features, to define areas that if restored through planting swamp species, the trees will likely survive long term. The Maurepas Land Bridge now has a large area that is “restoration ready”, and some small remaining areas, currently slated as areas of “future restoration” that seem to be shifting toward being suitable, indicated by decreasing soil and surface water salinities. LPBF and partners have successfully planted trees since 2013 in the restoration ready area here and the trees have 78% survival rate. One factor in the success of the tree plantings in Maurepas is the reduction in surface water salinity due to the MRGO closures in 2009. The other large area which is “restoration ready” is near the Caernarvon Freshwater Diversion. LPBF and partners have been planting trees here since 2010 and the trees have a 70% survival rate. Due to the vast areas now suitable for swamp restoration, LPBF is testing other restoration techniques such as aerial seeding.

About Us

LPBF's Vision is an environmentally sustainable, prosperous, and resilient region. Our mission is to drive environmental sustainability and stewardship through scientific research, education, and advocacy.

The Lake Pontchartrain Basin Foundation is a non-profit organization consisting of a 13-member board of directors representing Basin parishes and regulatory agencies. LPBF does not discriminate on the basis of race, color, national origin, sex, age, or disability.